Process for coating copper with vinyl resins



Patented Mar. 25, 1947 PROCESS FOR COATING COPPER WITH VINYL RESINSGeorge M. Powell, 3d, South Charleston, W. Va., and Earl F. Carlston,Arlington, Va., assignors to Carbide and Carbon Chemicals Corporation, acorporation of New York No Drawing. Application October 2, 1943, SerialNo. 504,714

1 Claim. 1

Vinyl resins which contain free hydroxyl groups attached to themacromolecule may be divided into two classes. One type of such resins,of which polyvinyl alcohol is an example, contains suflicient hydroxylgroups to be soluble in Water. The partial esters and partial acetals ofpolyvinyl alcohol in which sufllcient hydroxyl groups are leftunreacted, are also dispersible in water. However, such water-solubleresins are relatively insoluble in organic solvents. Another class ofhydroxylated vinyl resins are those which contain insufiicient hydroxylgroups to be soluble or dispersible in water. In general, these latterresins are soluble in organic solvents, such as alcohols.

It has previously been proposed to render polyvinyl alcohol, and itswater-soluble partial esters and acetals, insoluble in water bytreatment of the resins with certain insolubilizing agents, such ascompounds of metals oi the 6th and 8th groups of the periodic tables.

It has now been found that the water-insoluble, hydroxylated vinylresins may be rendered insoluble in organic solvents by heating themwith a copper compound at high temperatures. The copper compounds do notembrittle the resins under these conditions, whereas, salts of iron,chromium, manganese, cobalt and nickel cause the resins to becomebrittle under severe heating.

In another method of practicing the invention, the copper compound isnot employed directly, but the water-insoluble hydroxylated vinyl resinis applied as a film to a surface of metallic copper along with ammoniaor an amine. The ammonia or amine apparently dissolves or chemicallyattacks some of the copper surface, and the dissolved copper appears todiffuse into the resinous film. On heating the film to a hightemperature, insolubilization of the resin occurs as before, a

protective coating on the copper surface being formed.

To secure the maximum insolubilization of the hydroxylated vinyl resin,the length of time the resin and copper compound are heated should beadjusted with respect to the temperature. At temperatures of 250 F. to325 F., a baking time of at least one hour seems required; at 350 F., atleast 30 minutes seems necessitated, but better results are secured byheating the resin and copper compound'for at least 15 minutes at 400 F.,or for minutes at 500 F. At temperaturesbelow 250 F., very little, ifany, insolubilization of the hydroxylated vinyl resin occurs, althoughsolutions of the resin in organic solvents often gel upon the additionof a copper salt; but such a phenomenon does not correspond to trueinsoluq point of the film.

The copper atom appears to be the agent efiecting insolubilization, andthe salt group or complex to which it is attached serves only as a meansof incorporating the copper atom with the resin. Thus copper complexes,such as-cuprammonium hydroxide and cuprammonium sulfate may be employed.Also, both organicand inorganic salts of copper have been tested andfound effective. Copper acetate, copper Z-ethylhexoate, copper sulfate,copper chloride and copper. nitrate, all caused insolubilization ofhydroxylated vinyl resins on heating. Films containing copper acetateappeared to have the best resistance to water. The amount of the coppercompound employed may be varied, but generally about live to twentyparts of the copper compound per one hundred parts of the hydroxylatedvinyl resin are employed.

In the embodiment of the invention in which the hydroxylated vinyl resinis applied in solution form to a copper surface, and some of the copper.solubilized or attacked by the ammonia or amines, many amines have beentested and found effective, the firsteight listed below being moreeffective than the succeeding ones. These amines include diethanolamine,triethanolamine, morpholine, monoamylamine, dibenzylamine,di-2-ethylbutylamine, aniline, cyclohexylamine, N,N dihydroxyethylethylenediamine, N,N' tetrahydroxyethyl ethylenediamine, hydroxyethyldiethyl amine, propylene diamine, triethylene diamine, ethylene diamine,p-phenylenediamine, monoethanolamine, monoisopropanolamine,di-2-ethylhexenyl amine, di-2-et'nylhexyl amine and hexamethylenetetramine. The proportions of amine which may be employed may be variedfrom about 10 to 20 parts of amine per parts of the vinyl resin. Smalleramounts of ammonia may be used, proportions of 6.5 to 20 parts of a'28%aqueous ammonia solution per 100 parts of resin being typical.

The types of hydroxylated vinyl resins to which this invention isapplicable include water-insoluble, partially hydrolyzed polyvinylesters, and

water-insoluble polyvinyl acetal resins containing unreacted hydroxylgroups. The degree of hydrolysis of the former resins, that is, thepercentage of ester groups of the macromolecule which are hydrolyzed tohydroxyl groups, may vary from about 10% to about 40%. These resins maybe manufactured by dissolving the polyvinyl ester in an inert, anhydroussolvent, such as acetone, toluene or methyl acetate, adding an anhydrousalcohol, such as methanol, in the calculated proportions to give thedesired degree of alcoholysis (hydrolysis) and causing the reaction tooccur in the presence of an acidic or alkaline catalyst at temperaturesof 30 to 60 C. Typical polyvinyl esters which may be partiallyhydrolyzed include polyvinyl acetate, polyvinyl propionate, polyvinylbutyrate and polyvinyl benzoate.

Water-insoluble polyvinyl acetal resins containing unreacted hydroxylgroups may be made by known methods, such as by reacting polyvinylalcohol with an aldehyde or simultaneously hydrolyzing a polyvinyl esterand reacting it with an aldehyde. For each resin, the degree ofacetalization must be correlated with the ty of aldehyde reacted so thatwater-insoluble products result. In general, the degree of acetalizationmust be higher, the lower the molecular weight of the aldehyde reacted,in order to form waterinsoluble products. 'By the degree ofacetalization is meant the percentage of hydroxyl groups, consideringthe polyvinyl acetal resin as a derivative of polyvinyl alcohol, whichare reacted with aldehydes. The remaining hydroxyl groups are eitherunreacted or partially esterified. The following are examples ofwater-insolub e polyvinyl acetal resins containing unreacted hydroxylgroups:

Polyvinyl formal resins, approximately 95% acetalized, remaininghydroxyl groups substantially unreacted.

Polyvinyl formal resins, approximately 77.9% acetalized, 13.4% ofhydroxyl groups unreacted, and 8.7% of hydroxyl groups esterifled withacetic acid.

Polyvinyl acetal resins, approximately 85 to 94% acetalized, remaininghydroxyl groups substantially unreacted.

Polyvinyl propional resins, approximately 52 to 92% acetalized,remaining hydroxyl groups substantially unreacted.

Polyvinyl butyral resins, approximately 42 to 90% acetalized, remaininghydroxyl groups substantially unreacted.

Polyvinyl valeral resins, approximately 33 to 90% acetalized, remaininghydroxyl groups substantially unreacted.

Polyvinyl hexal resins, approximately 31 to 90% acetalized, remaininghydroxyl groups substantially unreacted.

On adding a copper compound to a solution of one of these hydroxylatedvinyl resins, gelation of the solution is frequently observed. However,the hydroxylated vinyl resin is not converted to a form resistant tosolvents untilafter the appropriate heat treatment. The cause of suchgelatlon is not clearly understood, since gelled solutions often becomefluid again upon adding an excess of the copper compound, Also, the gelsmay be liquefied by adding certain reagents, such as acetic acid, aceticanhydride, ammonia, amines, or ammonium acetate. The degree or tendencytowards gelatlon also depends on the particular copper compoundemployed, For instance, cuprammonium hydroxide does not cause gelationof the resin solution when excessive amounts are avoided, but copperacetate causes gelation even in small amounts. However, theeffectiveness of an insolubilizing agent cannot be judged by its effecton the consistency of solutions of the hydroxylated vinyl resins. Forinstance, solutions of these resins will gel when calcium acetate isadded, but the resins'contalning this salt do not become insoluble onbaking.

The tendency toward gelation upon the addi-- tion of a copper compoundalso varies with the particular vinyl resin which is dissolved. Forinstance, the polyvinyl acetal resins seem less sensitive than thepartially hydrolyzed polyvinyl esters.

The invention finds its most useful embodiment in the application ofhard, adherent and solventresistant coatings to various surfaces. Wherematerials other than copper are to be coated, such as surfaces of iron,tin plate, and zinc, a copper compound is included in the coating. Incoating copper or copper plated surfaces, ammonia or an amine isincluded in the coating composition to dissolve or activate part of thecopper necessary for insolubilization. Thus, the composition may beemployed to coat copper wire, chemical apparatus made of copper, such asbalance pans, and

copper reaction vessels. Since the compositions have good electricalinsulatin properties, very useful wire enamels for copper wire may bevformed containing a hydro-xylated vinyl resin,

ammonia or an amine, and a solvent. Such wire enamels may be applied inthe customary manner, the final heat treatment being a very brief one ata temperature of 800 F.

The composition may also be applied to surfaces other than metal, whichwill withstand the heat treatment required. Thus, heavy grades of papermay be impregnated with a heat-resistant coating by spreading thehydroxylated vinyl resin and the copper salt over the surface, and thenbaking the paper for 30 to seconds at 250 F., followed by a bake ofabout 5 to 10 seconds at 400 F. The compositions may also serve assolvent-resistant adhesives for joining articles of paper, cloth, wood,metal, leather and other materials.

The following examples will serve to illustrate the invention:

Example 1 A solution of the following composition was prepared:

Parts Partially hydrolyzed polyvinyl acetate (ap- This composition wasapplied to a clean copper panel by spraying. Almost immediately the filmbecame tinged with a bluish-green color indicating that the copper wasbeing attacked by the ammonia. After drying the panel for about 10minutes, it was placed in an oven at 400 F. for 12 minutes. After theheat treatment, the film of resin became much harder, tougher and moreadherent, and it assumed a brownish tinge. The baked film showedexcellent resistance to acetone and other ketones, to ethylenedichloride, to toluene, to alcohols and to transformer oil. Immersingthe coated panel in boiling water for two days did not loosen or softenthe film.

Example 2 The composition shown in Example 1 was sprayed over an ironpanel which had been previously electroplated with a thin film ofcopper. After baking the panel for 10 minutes at 400 F., a filmresistant to'acetone and boiling water was obtained.

Example 3 .The composition of Example 1 was applied by spraying to'aniron panel that had been copperplated by immers in an acidified bath ofcopper sulfate. Af i kbaking the panel at 400 F. for 10 minutes, a filmresistant to boiling water and to acetone was obtained.

Example 4 A copper strip was cleaned and then dip-coated with thefollowing solution:

Parts Partially hydrolyzed polyvinyl acetate (approximately 16%hydrolyzed) 15 Methyl acetate 28 Methanol 57 After air-drying, thecoated strip was immersed in a cuprammonium hydroxide solutionpreviously prepared by dissolving copper in 28% aqueous ammonia,bubbling air free of carbon dioxide through the solution for 18 hoursand then filtering. After an immersion of five Eaample 5 The followingcomposition was prepared:

' Parts Partially hydrolyzed polvinyl acetate (approximately 29%hydrolyzed) 9.6 Methyle acetate 17.9 Methanol 15.5 Diethylene glycolmono-butyl ether 32 Water 21 Ammonia (28% solution in water) 4 Thiscomposition was applied to a clean copper panel by spraying. The filmbecame tinged with a bluish-green color indicating that some of thecopper was being attackedby the ammonia. After drying the panel, it wasplaced in an oven at 400 F. for ,12 minutes. After the heat treatment,the film of resin became much harder, tougher and more adherent. Thebaked film showed outstanding resistance to acetone and other ketones,to ethylene dichloride, to toluene, to alcohols and to transformer oil.Immersing the coated panel in boiling water for two days did not loosenor soften the film.

Example 6 A solution of the following composition was prepared:

- Parts Partially hydrolyzed polyvinyl acetate (approximately 16%hydrolyzed) 9.8 Methyl acetate 17.9 Methanol 15.5 Diethylene glycolmono-butyl ether 32 Water 21 Diethanolamine 3 This composition wasapplied to a clean copper panel by spraying. The film became tinged witha bluish-green color indicating that the copper was being attacked bythe diethanolamine. After drying the panel, it was placed in an oven at400 F. for 12 minutes. After the heat treatment, the film oi. resinbecame much harder, tougher resistance to acetone and other ketones, toethylene dichloride, to toluene, to alcohols and to transformer oil.Immersing the coated panel in boiling water for two days did notappreciably loosen or soften the film.

Example 7. The following compositions were prepared:

Polyvinyl partial butgral resin (ap roximately- Parts Parts accta yzedwith utyraldchydeg 15 15 Methanol 110 110 Diethylene glycol mono-butylother. 100 100 Cupric acetate (10% aqueous solution l4 We r l4 Glacialacetic acid l 1 Two panels of black iron were thoroughly cleaned andfilms of the above resin were deposited on the panels from therespective solutions. Both films were than baked at 100 F. for 20minutes. The coating on panel A was much more resistant to acetone andto hot water than the coating on panel B.

Example 8 The following .composition was prepared:

This composition was applied to a clean black iron panel and the coatingthen baked at 400 F. for 15 minutes. After baking, the coating wasresistant to dioxane and methanol.

Example 9 This example illustrates the fact that the copper salts do notcause the hydroxylated vinyl resins to become brittle on baking as doother insolubilizing agents. To show this, films of equal thickness of apolyvinyl partial butyral resin, approximately 70% acetalyzed withbutyraldehyde, containing various metal salts were cast on glass. Themetal salts tested were copper acetate, manganese acetate, chromiumacetate, cobalt acetate, nickel acetate, zinc acetate, lead acetate, andmercury acetate. Each film, as well as a control film, containing nometal salt was baked at 450 F. for 15 minutes. The amount of cupricacetate employed amounted to about 10% of the resin and the amounts ofthe other metal salts were based on the molar equivalents. This made asignificant difference in the amounts employed ,of the metal saltscomputed on a weight basis only in the case of lead acetate and mercuryacetate.

After baking the'films they were removed from the panels by steaming.The control film of untreated resin and the cupric acetate treated resinhad about equal adhesion and required a considerable steaming period torelease them from the glass, whereas all the other films strippedeasily. Observation of the films showed that only the film containingthe copper salt was as flexible as the control film and all the otherfilms were more brittle. The vast majority of them were too brittle tohandle and broke on slight and more adherent. The baked film showed goodflexure.

Example The following composition was prepared:

' Parts Polyvinyl partial butyral resin 168 Triethylene glycoldi(2-ethylhexoate) 68 Copper 2-ethylhexoate 10 This composition wasdispersed on a heated roll mill to form a resilient, elastic sheethaving a. green color. On baking the sheet at 250 F. for one hour, itbecame insoluble in alcohol, but did not lose its elasticity andresilience. Other plasticizers may, of course, be substituted for theone illustrated herein, such as dibutyl sebacate, tricresyl phosphateand triethylene glycol di 2-ethylbutyrate) Such compositions may bedissolved in solvents, such as alcohols, and applied to cloth. Afterbaking the cloth, an alcohol-insoluble, flexible coating of reducedthermoplasticity and increased resistance to water is formed. The coatedcloth may be fashioned into raincoats and other articles prior to theinsolubilization treatment.

The foregoing examples are intended to illustrate the principles of theinvention, and many variations in the compositions, other than asspecifically shown, are included within the scope of the invention. Forinstance, dyes, pigments, waxes, oils, plasticizers, synthetic gums,elastomers, and synthetic resins, may be included in the compositions asis customary in compounding vinyl resin coatings.

We claim:

Process for coating articles having a copper surface which comprisesapplying to the copper surface, a solution containing an organicsolvent, water, ammonia, and one of the group consisting ofwater-insoluble partially hydrolyzed polyvinyl esters, andwater-insoluble polyvinyl acetal resins containing free hydroxyl groups,permitting the liquids of the solution to remain in contact with thecopper surface until a bluish-green color is observed heating theapplied coating at a temperature of at least 325 F., and forming anadherent, alcohol-insoluble film on said surface.

GEORGE M. POWELL, 3RD. EARL F. CARLSTON.

REFERENCES CITED The following references are of record in the tile ofthis patent:

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